//The DNA strand is missing the pairing element. Take each character, get its pair, and return the results as a 2d array.Base pairs are a pair of AT and CG. 
function pairing( str ) {
  const paired = {
    "A": "T",
    "T": "A",
    "G": "C",
    "C": "G"
  };
  return str.split( "" ).map( x => [ x, paired[ x ] ] )
}
console.log( pairing( "ATCGA" ) ) //[["A","T"],["T","A"],["C","G"],["G","C"],["A","T"]]

//OR Using Switch statement
// function pairElement(str) {
//     var empty = [];
//     function search(char) {
//       switch(char){
//         case "A":
//        empty.push(["A","T"]);
//        break
//      case "T":
//        empty.push(["T","A"]);
//        break
//        case "G":
//        empty.push(["G","C"])
//        break
//        case "C":
//        empty.push(["C","G"])
//       }}
//     for(let i=0; i<str.length; i++){
//     search(str[i])
//     }
//     return empty
//     }
